The present invention relates to apparatus for internal welding of pipes or like objects in general, and in particular to a device for producing circumferential internal welding seams in pipes of greater diameters and length.
There are known apparatus for producing internal welding seams in the pipes which are rotated about their central axes. The pipes to be treated are normally placed on a rotating mechanism and the circumferential seam welding is performed on those pipes by the welding equipment. The welding apparatus itself is held in the stationary position while the pipes are turned about their axes by the rotating mechanism. The welding is carried out from outside of the pipe and therefore the welding apparatus can be easily held in the stationary position or moved longitudinally of the pipe. However, in many instances a welding exclusively from outside of the pipe is not possible and an additional welding from inside of the pipe is required. Moreover, for long pipes such as used for long-distance pipelines, it has been difficult to get to the point to be welded with a suitable automatic welding equipment.
The internal welding of pipes is disclosed, for example in U.S. Pat. No. 4,238,659. In the reference method the welding torches are mounted at the free end of a boom which is laterally moved into the pipe to be welded. The boom is moveable by a carriage so that the end of the boom carrying the welding torches is inserted into the pipes to be welded. The boom is mounted to the carriage so that it can be adjusted in height.
The disadvantage of this otherwise satisfactory apparatus is that vibrations may occur during the operation of the welding equipment on relatively long pipes due to the length of the boom which must be sufficient to move the welding torches to the necessary point, these vibrations can cause difficulties for a regular welding. Furthermore, there are restrictions in a possible length of the boom since it can not be extremely long.
A device for internal welding is also disclosed in USSR Inventors' Certificate No. 735,389 which describes an internal welding installation mounted within the pipe being treated. A circumferential weld is carried out by means of a welding equipment driven by a special drive. During this process the welding equipment is rotated about the central axis of the pipe whereas the pipe to be welded is stationary. The disadvantage of this design is that the welding position is constantly changing during the process of circumferential welding. This has negative effects on the quality of the weld being produced. Moreover, all known welding methods especially submerged-arc welding which is used very often due to its efficiency cannot be utilized with this known device.